SALT LAKE CITY — Yes, Amed Rosario has himself a motto, a mantra, before he has even played in a major league game.

“Don’t be surprised,” the Mets’ highly touted shortstop preaches, hash tag included, on many of his social-media posts. “Be ready.”

“That’s something that we came up with a couple of years ago,” Ulises Cabrera, Rosario’s agent, said this past week in a telephone interview. “Prepare yourself for success. Don’t be surprised when it comes. It’s been a motivating factor for him, and a guiding light for him, as he ascends to the highest level that he can reach, whether that’s [currently] Triple-A or the big leagues. He’s keenly focused on being as good as he can be.”

Ah, but it turns out Rosario, the 21-year-old whom four different media outlets ranked among their top 10 preseason prospects, views his catch phrase with a more self-assured twist. A little mischievous, even.

Quite simply, he told The Post, “People shouldn’t be surprised” by what he can do.

So this doesn’t constitute mere general advice. It is a warning, specifically, that the rest of us had best be prepared for what Rosario will bring to the party. Very likely at some point this season.

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“I’m always trying to be ready. I’m always ready to go for whatever,” Rosario elaborated, through an interpreter, in one of two recent interviews at Smith’s Ballpark during a series between his Las Vegas 51s and the Salt Lake Bees (the Angels’ Pacific Coast League affiliate). “So they shouldn’t be surprised.”

If Rosario wasn’t literally born ready, it didn’t take him too long to get there. Rosario’s father, German, an attorney and then a judge in the Dominican Republic’s capital Santo Domingo Centro, grew up a baseball nut, learning about the game from his grandfather Radame Dilone and his father, Lorenzo Rosario. German Rosario’s wife, Nerys, also a white-collar worker, started their family by giving birth to two girls.

“And then the third one came around, and that was Amed, our boy,” German Rosario said in a telephone interview, through an interpreter. “When he came around, I knew that was our chance to have my father and my grandfather’s dream of a baseball player. So I started working with him from a young age.”

RosarioRosario family

The training, German Rosario said, began at home when Amed was 2. The father asserted that he realized his son’s vast potential by age 4.

“I knew it then because we would take around 200 swings a day,” German said. “We used a sort of palm leaf sometimes to use as a bat to swing, and we would swing at things as small as grains of beans or corn kernels. He could run about a kilometer warming up.”

School ranked as a priority in the Rosario home.

“Whenever we were in the midst of tryouts, because he had so many tryouts, his mother would keep him doing work at home,” German Rosario said. Yet though Amed Rosario created more options for himself by graduating high school, an accomplishment many young Dominican players eschew in order to focus on a professional contract, “This is really where it’s always been at for me,” he said, referring to baseball.

“From the beginning, he knew what he wanted,” Gerardo Cabrera, a Mets coordinator of Latin American scouting, said in a telephone interview. “He was a really smart kid with a lot of desire and a work ethic. … He really enjoyed playing baseball.”

He loved watching it, too, and he came of age during a time when his fellow Dominicans David Ortiz and Manny Ramirez formed the most imposing hitter duo of their era.

“I think everything you heard over there was between the Red Sox and the Yankees and that rivalry being just such a big rivalry. It’s what people talked about,” Amed Rosario said. “Back then, the Red Sox were my favorite team.”

Rosario with the 51sScott Sommerdorf

The Mets were on his radar, too. He liked watching Latino players like Carlos Beltran, Carlos Delgado, Jose Reyes and Johan Santana. The Mets gained their real edge in this sweepstakes, though, when Cabrera first set eyes on Rosario as a 13-year-old, and began to establish a relationship with the family. A couple of months before the July 2, 2012, launch date for Rosario’s age group (players who have turned 16 in the prior year) to sign with a team, Cabrera set up a workout for Rosario in front of Mets bosses Chris Becerra and Paul DePodesta. Given Rosario’s busy playing schedule, he and the Mets agreed to hold the personal showcase at 6:30 a.m.

“I had to wake up at like 5 in the morning,” Rosario said. “I remember that the guy who used to train me back then, when he got to my house, it was so early that everyone else was still sleeping. So I opened the door, and he kind of crashed on the couch for a little bit before we got going.”

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“I’ll never forget that day,” Cabrera wrote in a text message, “because [Rosario] did a pretty good job.”

Pretty good enough that the Mets paid him a $1.75 million signing bonus, the highest of any Latin American prospect that year. German Rosario, who handled the bulk of the negotiations, said the family also considered strong offers from the A’s, Rangers and Cardinals.

“But because we had a familiarity with the Mets, and just knew them a little bit more, [that] is the reason we ultimately went with them,” said German Rosario, who credited Cabrera and Becerra for establishing a bond with the family.

And really, it has been pretty smooth sailing up the organizational ladder for Amed Rosario. Always a gifted defender, he steadily has improved his offense and uses his blazing speed to enhance his batting average.

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In his first professional season, 2013, the Mets assigned him to their Rookie League affiliate in Kingston, Tenn. Rosario recalled sitting at a restaurant in the area and not being able to order anything.

“They sent me out there so far, kind of in the middle of nowhere,” Amed Rosario said. “I was so young. I was 17. In my mind, I was thinking, ‘I need to learn English or I’m going to starve.’ ”

He now can communicate easily with all of his teammates and coaches, relying on an interpreter only for longer media sessions.

“He definitely doesn’t act his age,” 51s catcher Kevin Plawecki said of Rosario. “As young as he is, he has a confidence about him. And that’s the biggest thing, carrying yourself. Staying humble at the same time, which he does. That’s obviously good to see.”

RosarioScott Sommerdorf

He carries himself with a strong enthusiasm for his profession, whether he is bopping along to salsa music as he takes grounders at shortstop in pregame drills or exhibiting his remarkable range and quickness on a challenging play up the middle.

“He’s a 21-year-old kid that still plays the game like a 17-year-old senior in high school,” said Jack Voigt, the 51s’ hitting coach. “You watch him take groundballs, that’s what he’s like every day.”

“I just truly enjoy this game,” Amed Rosario said. “I try to have fun every time I’m out on the field.”

The most fun, he knows, is yet to come.

“I feel like I’m ready [for the major leagues],” he said. “But it’s all about timing, and it’s all about God’s timing. Whenever that chance comes up.”

And when it does, probably pretty soon, he will be ready. With his game. With his approach. Yes, with his social-media savvy. He even will have familial support, with one older sister, Zulima, already living in Queens and the other, Yanitza, in The Bronx (a younger sister, Aniana, lives in the Dominican).

“The one in Queens is two [subway] stops away from the ballpark,” said Rosario, who apparently already knows his way around the 7 line.

He is ready. He has done his best to not be surprised. We should do the same.